A brake system may be used to decelerate or restrict movement of a vehicle. A disc brake system is a common type of brake system. During a standard brake apply in a disc brake system, fluid is pressurized, which causes one or more brake pistons to move one or more brake pads against a brake rotor to create a clamping force. The clamping force may function to decelerate or restrict movement of the vehicle. To release the brake apply and/or release the clamping force, the fluid is depressurized and, accordingly, the one or more brake pistons and brake pads move away from the brake rotor. Once released, the vehicle is free to move again.
A parking brake system may utilize one or more components of the brake system to maintain a vehicle in a stopped or parked position. In modern applications, the parking brake system may be an electromechanical system. An exemplary electromechanical parking brake system includes one or more motor gear units and one or more linkages. A linkage may comprise a spindle and a nut. The nut may be keyed to an inner portion of a brake piston (i.e., to a piston pocket) so that the nut and the brake piston are restricted from independently rotating relative to one another.
During a parking brake apply in an exemplary electromechanical parking brake system, the motor gear unit may rotate the spindle in a first direction, which may cause the nut to translate axially and push the corresponding brake piston towards and eventually into contact with one of the brake pads to develop the clamping force to maintain the vehicle in a stopped or parked position. To release the parking brake and/or the clamping force, the motor gear unit may rotate the spindle in an opposite direction so that the nut and the corresponding brake piston move away from the brake pad so that the brake pads can move away from the brake rotor so that the vehicle is free to move again.
While the aforementioned parking brake system has proven satisfactory, opportunities for improvement may exist. For example, because the nut is keyed to the inner portion of the brake piston, properly aligning the nut with the brake piston during assembly can be time-consuming and cumbersome. Also, for example, during release of the parking brake, once the nut can no longer axially move (i.e., once the nut and the spindle thread stop make contact), further rotation of the spindle by the motor gear unit may undesirably cause the nut to rotate the brake piston, which may tear or otherwise damage the piston boot That surrounds the brake piston. Moreover, for example, damage may occur to the motor gear unit, the linkage, or both if the motor gear unit continues to rotate the spindle, but the nut is restricted from axially moving.
Accordingly, it may be desirable to have an improved parking brake system, an improved brake piston, an improved linkage, or a combination thereof. It would be attractive to have a nut that is not keyed to an inner portion or pocket of the brake piston, but can still be used to develop the clamping force necessary to maintain a vehicle in a stopped or parked position. It may be desirable to have a spindle and a nut that can be quickly and easily assembled together. It may be attractive to have a nut that is not keyed to an inner portion of the brake piston so that assembly time of the nut and the brake piston can be improved. It may be attractive to have a nut that is not keyed to an inner portion of the brake piston but is still restricted from rotating within the inner portion of the brake piston during a parking brake apply and/or during release of the parking brake. It may also be attractive to have a nut that can be restricted from rotating within the inner portion of brake piston when there is no clamping force or while the clamping force is being created, but allowed to rotate therein once the frictional engagement between the spindle and the nut is greater than the frictional engagement between the nut and the piston pocket, or, preferably, between a nut seal and an inner pocket wall.